We report on the formation of titania (TiO2) colloids via the hydrolysis and condensation of alkoxides under a large excess of water. This process is characterized by a rapid precipitation of large aggregates, followed by a slow peptization (deaggregation) induced by the presence of nitric acid. We find that the hydrolysis temperature and the length of the alkoxy group have a minor effect on the size of the peptized colloid. In contrast, the particle size is sensitive to the peptization temperature and exhibits a minimum at 50|SDC. The presence of alcohols inhibits peptization and results in both larger colloids and longer peptization treatments. The smallest size (~20 nm in diameter) is obtained when no alcohol is added to the reaction mixture. The results suggest that the formation of TiO2 nanoparticles is controlled by colloidal interactions, whereas chemical factors (the rate of hydrolysis and condensation) have a secondary role.
We report on the effect of alcohols in the acid peptization of aggregated titania nanoparticle produced from alkoxides. Peptization was studied in the presence of each one of the following alcohols: methanol, ethanol, propanol and isopropanol. We find that the final particle size is correlated to the dielectric constant of the peptizing medium. Kinetic measurements reveal that the rate of deaggregation is not affected by the presence of alcohol; however, the tendency for reaggregation of the peptized colloid increases significantly. We conclude that alcohols prevent the full redispersion of the aggregates by decreasing the colloidal stability of the suspension. This conclusion is supported by the measured zeta potential of the peptized particles, which is found to decrease when alcohol is present.
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